It has long been desirable to provide drivers with occupancy data concerning parking lots in order to assist them in finding an available parking space as quickly and conveniently as possible. Traditionally this has been achieved by installing physical apparatus such as cameras, parking kiosks, road sensors or entry and exit barriers at the parking lots. Information collected using this apparatus may then be electronically communicated to display boards distributed throughout a city or potentially uploaded to a server for users to access remotely via a portable device connected to the Internet.
Whilst this method has the advantages that the data provided is live and is reasonably accurate, the apparatus required to generate the occupancy data is typically expensive to install and for this reason is not always provided. Indeed this is typically the case where parking is provided free of charge, for example outside large supermarkets or retail parks. It would be desirable, however, for interested parties including retailers to still be able to monitor how busy their parking lot is so that they can take appropriate steps such as expanding their parking lot if necessary in order to attract more customers during busy periods or provide for shared use with other organisations during low occupancy periods. Furthermore, even if occupancy data is generated, this information may be kept private for the benefit of the owner of the parking lot only and not widely distributed. It would nonetheless be useful for retailers to be able to monitor the occupancy of a competitor's parking lot during different months of the year or times of day, for example, in order to estimate how busy their store is.
More recently it has been suggested that parking occupancy data could be generated by portable devices that emit “probe data” indicating the position of the device at a given point in time. For instance, a server may collect probe data from within a parking area via a mobile telephone network and compare this to an estimated fraction of vehicles equipped with a Portable navigation device (PND), to produce an estimate of the number of available parking spaces. An estimate of the average number of PNDs per vehicle can be obtained, for example, by monitoring probe data received from traffic jams across a known stretch of road containing a known number of vehicles. This can then be used to estimate the number of occupied parking spaces within a parking lot. The occupancy data generated by this method is typically unreliable however as the number of vehicles that contain a device actively emitting probe data within the lot typically deviates significantly from the assumed average. It is thus desirable to provide an improved method that overcomes the abovementioned deficiencies in the prior art.